org.apache.jackrabbit.oak.plugins.segment

Class InMemoryCompactionMap

java.lang.Object

org.apache.jackrabbit.oak.plugins.segment.InMemoryCompactionMap

All Implemented Interfaces:

PartialCompactionMap

public class InMemoryCompactionMap
extends Object
implements PartialCompactionMap

Immutable, space-optimized mapping of compacted record identifiers. Used to optimize record equality comparisons across a compaction operation without holding references to the SegmentId instances of the old, compacted segments.

The data structure used by this class consists of four parts:

1. The recent map of recently compacted entries is maintained while the compaction is in progress and new entries need to be added. These entries are periodically compressed into the more memory-efficient structure described below.
2. The msbs and lsbs arrays store the identifiers of all old, compacted segments. The identifiers are stored in increasing order, with the i'th identifier stored in the msbs[i] and lsbs[i] slots. Interpolation search is used to quickly locate any given identifier.
3. Each compacted segment identifier is associated with a list of mapping entries that point from a record offset within that segment to the new identifier of the compacted record. The entryIndex array is used to to locate these lists within the larger entry arrays described below. The list of entries for the i'th identifier consists of entries from entryIndex[i] (inclusive) to entryIndex[i+1] (exclusive). An extra sentinel slot is added at the end of the array to make the above rule work also for the last compacted segment identifier.
4. The mapping entries are stored in the beforeOffsets, afterSegmentIds and afterOffsets arrays. Once the list of entries for a given compacted segment is found, the before record offsets are scanned to find a match. If a match is found, the corresponding compacted record will be identified by the respective after segment identifier and offset.

Assuming each compacted segment contains n compacted records on average, the amortized size of each entry in this mapping is about 20/n + 8 bytes, assuming compressed pointers.

Method Summary

Methods

Modifier and Type	Method and Description
void	compress() Compressing this map ensures it takes up as little heap as possible.
RecordId	get(RecordId before) Retrieve the record id before maps to or null if no such id exists.
long	getEstimatedWeight() The weight of the compaction map is its heap memory consumption in bytes.
long	getRecordCount() Number of records referenced by the keys in this map.
long	getSegmentCount() Number of segments referenced by the keys in this map.
boolean	isEmpty() Determine whether this map contains keys at all.
void	put(RecordId before, RecordId after) Adds a new entry to the compaction map.
void	remove(Set<UUID> uuids) Remove all keys from this map where keys.contains(key.asUUID()).
boolean	wasCompacted(UUID id) Checks whether content in the segment with the given identifier was compacted to new segments.
boolean	wasCompactedTo(RecordId before, RecordId after) Checks whether the record with the given before identifier was compacted to a new record with the given after identifier.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

wasCompactedTo

public boolean wasCompactedTo(@Nonnull
                     RecordId before,
                     @Nonnull
                     RecordId after)

Description copied from interface: PartialCompactionMap

Checks whether the record with the given before identifier was compacted to a new record with the given after identifier.

Specified by:

wasCompactedTo in interface PartialCompactionMap

Parameters:

before - before record identifier

after - after record identifier

Returns:

whether before was compacted to after

wasCompacted

public boolean wasCompacted(@Nonnull
                   UUID id)

Description copied from interface: PartialCompactionMap

Checks whether content in the segment with the given identifier was compacted to new segments.

Specified by:

wasCompacted in interface PartialCompactionMap

Parameters:

id - segment identifier

Returns:

whether the identified segment was compacted

get

public RecordId get(@Nonnull
           RecordId before)

Description copied from interface: PartialCompactionMap

Retrieve the record id before maps to or null if no such id exists.

Specified by:

get in interface PartialCompactionMap

Parameters:

before - before record id

Returns:

after record id or null

put

public void put(@Nonnull
       RecordId before,
       @Nonnull
       RecordId after)

Description copied from interface: PartialCompactionMap

Adds a new entry to the compaction map. Overwriting a previously added entry is not supported.

Specified by:

put in interface PartialCompactionMap

Parameters:

before - before record id

after - after record id

remove

public void remove(@Nonnull
          Set<UUID> uuids)

Description copied from interface: PartialCompactionMap

Remove all keys from this map where keys.contains(key.asUUID()).

Specified by:

remove in interface PartialCompactionMap

Parameters:

uuids - uuids of the keys to remove

compress

public void compress()

Description copied from interface: PartialCompactionMap

Compressing this map ensures it takes up as little heap as possible. This operation might be expensive and should only be called in suitable intervals.

Specified by:

compress in interface PartialCompactionMap

getSegmentCount

public long getSegmentCount()

Description copied from interface: PartialCompactionMap

Number of segments referenced by the keys in this map. The returned value might only be based on the compressed part of the map.

Specified by:

getSegmentCount in interface PartialCompactionMap

Returns:

number of segments

getRecordCount

public long getRecordCount()

Description copied from interface: PartialCompactionMap

Number of records referenced by the keys in this map. The returned value might only be based on the compressed part of the map.

Specified by:

getRecordCount in interface PartialCompactionMap

Returns:

number of records

isEmpty

public boolean isEmpty()

Description copied from interface: PartialCompactionMap

Determine whether this map contains keys at all.

Specified by:

isEmpty in interface PartialCompactionMap

Returns:

true iff this map is empty

getEstimatedWeight

public long getEstimatedWeight()

Description copied from interface: PartialCompactionMap

The weight of the compaction map is its heap memory consumption in bytes.

Specified by:

getEstimatedWeight in interface PartialCompactionMap

Returns:

Estimated weight of the compaction map